Conventional techniques have been developed for intravenous or intra-arterial delivery of a liquid to a patient by pumping or other form of pressurized delivery. Low flow rate applications may be accommodated by using a peristaltic pump or syringe pump. Such systems typically include disposable components manufactured from thermoplastic materials. It is difficult to manufacture such components relatively inexpensively and still maintain precise dimensional control of the components. When the components are used in a fluid delivery system for providing liquids at low flow rates (e.g., 0.1-100 ml/hr), the accuracy of the flow rate control may not be sufficiently great to permit the use of such a system in certain applications. Alternatively, relatively expensive manufacturing techniques must be employed to insure relatively close dimensional tolerances which would enable such a system to be operated with a more accurate flow control at low flow rates.
Pressurized container systems for delivering liquid typically employ a precision orifice for flow control. The flow rate is dependent upon, among other things, the source pressure, and that source pressure can change during the delivery process (e.g., the pressure may drop as the supply of the liquid is dispensed). In any event, it is difficult to manufacture such an orifice within tight dimensional tolerances. Typically, with a conventional orifice, the overall accuracy of the rate of delivery lies within a range of 20% to 50%. This obviously limits the applications for such orifice-controlled pressurized delivery systems to the delivery of those liquids, such as some drugs, where the accuracy of the flow rate is not critical.
It would be desirable to provide an improved monitoring and control system for liquid delivery at accurate, low flow rates. Such an improved flow monitoring and control system should preferably accommodate the use of relatively inexpensively manufactured components.
Further, it would be desirable if such an improved system could incorporate permanent control components which can be calibrated by the manufacturer and which can be manufactured at relatively low cost, but with the precision necessary to provide low flow rate control at the desired accuracy.
It would also be advantageous if such an improved system could incorporate a disposable cassette structure for receiving and dispensing the liquid.
Such an improved system should also desirably accommodate relatively small, portable designs that can be used by ambulatory and/or confined patients.
In addition, it would be desirable to provide an improved system that could accommodate the use of improved monitoring and recording capabilities for the current flow rate and the total volume of liquid delivered.
It would also be desirable to provide system controls having an accuracy sufficient to permit the delivery of drugs for use in pain management and other therapies which require long term, accurate delivery (e.g., within about 5% accuracy).
The present invention provides an improved liquid flow monitoring and control system which can accommodate designs having the above-discussed benefits and features.